1. Field of the Invention
This invention relates to an electrochemicl potential memory device formed of two electrodes containing an Ag.sub.2 Se-Ag.sub.3 PO.sub.4 solid solution, and an aqueous or non-aqueous electrolyte containing silver ion.
2. Description of the Prior Art
Investigations on Ag.vertline.RbAg.sub.4 I.sub.5 .vertline..beta.-Ag.sub.2 Se type cells have shown that cells of this type can be used as coulometers or memory devices as disclosed in Takahashi et al, [J. Electrochem. Soc., 118, 1051 (1971)]. Detailed study of the electrochemical properties of an Ag.sub.2 Se-Ag.sub.3 PO.sub.4 solid solution have been made as disclosed in Takahashi et al [J. Electrochem. Soc., 119, 1735 (1972)], it has been shown that Ag.vertline.RbAg.sub.4 I.sub.5 .vertline.Ag.sub.2 Se-Ag.sub.3 PO.sub.4 .vertline.RbAg.sub.4 I.sub.5 .vertline.Ag cells using this solid solution and a solid electrolyte can be used as analog memory devices. In this type of cell, one of the two Ag electrodes acts as a reference electrode.
An electrochemical memory device (Memoriode, trade name produced by Sanyo Electric) based on the application of this theory has been developed as disclosed in Ikeda et al [Sanyo Technical Review, 4, 3 (1972)], and the application of such a memory device to a timing apparatus is disclosed in U.S. Pat. No. 3,753,110.
In conventional electrochemical devices using an Ag.sub.2 Se-Ag.sub.3 PO.sub.4 solid solution, a silver electrode is used as a counter electrode and a solid electrolyte is used as an electrolyte. In this type of electrochemical device, when a current is passed between the Ag.sub.2 Se-Ag.sub.3 PO.sub.4 solid solution electrode and the silver electrode, and the voltage is simultaneously measured, an accurate value of the voltage cannot be obtained because of the resistance of the solid electrolyte or the polarization of the electrodes. In order to remove this defect, a reference electrode is employed. A current is passed between the Ag.sub.2 Se-Ag.sub.3 PO.sub.4 solid solution electrode and the silver electrode, and the voltage is measured between the Ag.sub.2 Se-Ag.sub.3 PO.sub.4 solid solution electrode and the reference electrode. These electrochemical potential memory devices have the following defects.
(1) In use, the electric circuit is complicated because three electrodes are involved.
(2) The relationship between the voltage and the quantity of electricity in the electrochemical device is not linear.
(3) The resistance is high because a solid electrolyte is used. Even if a reference electrode is employed, a large error in measurement occurs when a large current is passed.
(4) The operable voltage range is limited to that which is positive with respect to the reference electrode.